See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Electrophilic aromatic substitution (EAS) with Br2/Fe as a Lewis acid catalyst. The key is identifying which aromatic ring undergoes bromination and at which position. Step 1: Identify the aromatic rings in the molecule. The starting material is 2-phenylisoindolin-1-one. It contains two aromatic rings: (i) The benzo ring fused to the isoindolinone system (benzene ring fused to the lactam) (ii) The N-phenyl ring attached to the nitrogen Step 2: Assess the reactivity of each ring toward EAS. The benzo ring of the isoindolinone is fused to a five-membered lactam ring containing a carbonyl (C=O) adjacent to it. The carbonyl is electron-withdrawing by induction and resonance, making the fused benzene ring electron-poor (deactivated toward EAS). The N-phenyl ring: The nitrogen of the lactam is bonded to both the carbonyl carbon and the phenyl ring. In a lactam, the nitrogen lone pair is delocalized into the carbonyl (amide resonance), making the nitrogen a weaker electron donor. However, relative to the fused benzo ring (which is directly deactivated by the electron-withdrawing carbonyl), the N-phenyl ring is comparatively less deactivated. In fact, nitrogen in an amide still donates some electron density to the attached phenyl ring, making the N-phenyl ring more reactive toward EAS than the carbonyl-deactivated fused ring. Step 3: Determine the position of bromination on the N-phenyl ring. The nitrogen (even as an amide) acts as an ortho/para director toward the attached phenyl ring. With EAS occurring on the N-phenyl ring, substitution would be at the ortho or para position. Para substitution is strongly favored over ortho due to steric reasons (the bulky isoindolinone moiety at the nitrogen causes steric hindrance at the ortho positions). Therefore, bromination occurs at the para position of the N-phenyl ring. Step 4: Match to answer choices. Option (d) shows 2-(4-bromophenyl)isoindolin-1-one, where Br is at the para position of the N-phenyl group. This matches the prediction. Why other options fail: - Options (a) and (b): Bromination on the fused benzene ring of isoindolinone is disfavored because this ring is deactivated by the adjacent carbonyl. - Option (c): Br at C3 (the CH2 position) would require allylic/benzylic bromination conditions (e.g., NBS/light), not Br2/Fe which promotes EAS. Therefore, the correct answer is D.